1. Field of the Invention
The present invention relates to a printing system control method, and printing apparatus, more specifically, usage cases such as multiple printed media being stacked in massive numbers.
2. Description of the Related Art
In conventional printing, issuance of printed articles (sheets) has been performed through various processes. For example, there are processes such as receiving a document, application of a design as to this document, layout editing, comprehensive layout (presentation with printing), proofing (layout correction and color correction), proof printing, mechanical creating, printing, post-processing processes, sending, and so forth.
Also, in conventional printing, an offset reproduction printer has been employed at a printing process, which needs a mechanical creating process. However, a created mechanical cannot be readily corrected, so correction for a mechanical results in increase in costs. Accordingly, mechanical creating needs elaborate proofing, i.e., elaborate layout check, and elaborate color confirmation work. Therefore, it has taken a long time up to issuance of printed articles.
Also, there have been large-scale apparatuses employed for the respective processes, which need technical knowledge, and accordingly, a skilled person's expertise is vital to employ such apparatuses.
With regard to such a situation, in recent years, a POD (Print On Demand) printing system has been proposed (see USP publication-before-examination US-2004 No. 0190057), which employs a printing apparatus using electrophotography or printing apparatus using inkjet. Such a POD printing system eliminates necessity for such mechanical creating, and other complicated work.
However, in a case of assuming realization of such a POD printing system, various types of problems are expected. For example, with the POD market, mass-printed articles (sheets such as printed sheets) are continuously ejected, so there is employed a paper ejecting apparatus capable of stacking thousands of sheets. This paper ejecting apparatus is specifically a finisher (large-capacity stacker) with a dolly expected to handle mass-printed articles, and to employ an offline post-processing apparatus.
If mass-printed articles (e.g., 5000 sheets) according to the same document page (same image) are printed and stacked in the same direction continuously, the following problems are caused. Specifically, in the above-mentioned stacking mode, portions on which much toner (color material) is disposed land at the same position, which causes a great stacking height difference between a portion on which much toner is disposed and a portion on which little toner is disposed, even though the difference in thickness is slight on one sheet. As a result thereof, a problem is expected wherein a stacked sheet bundle becomes unstable in its stacked state, such that the stacked sheet bundle is inclined, or the sides at the time of stacking are curved or shifted, or the stacked sheet bundle shifts and falls. Further, if such a situation continues for long time, there is a possibility that bending of the stacked sheets will remain.
That is to say, though a slight thickness difference as to one sheet, if thousands of sheets are overlaid, the difference becomes several centimeters, which is not insignificant. For example, let us say that, such as a printed article 3101 shown in FIG. 31, 5000 sheets of printed articles (the printed contents may differ) where an image on which much toner is disposed is printed on the left side, and a text image on which little toner is disposed is printed on the right side, have been stacked continuously.
In this case, in a state in which the sheets have been stacked, for example, the left side on which much toner is disposed is a stacking height of 110 cm, but the right side on which little toner is disposed is a stacking height of 103 cm, and accordingly, there is a possibility that a problem will be caused for the sheet bundle such as inclination, shifting, shifting and falling, bending, or the like.
Accordingly, stacking a massive number of sheets, on which images where much toner is disposed at the same position are printed, continuously in the same ejecting destination, has to be avoided.